More Russian troops have arrived in Belarus for military training, prompting anxiety in Ukraine.
Some 9,000 Russian soldiers are expected to be stationed in Belarus for what is officially described as "exercises".
But the troop movement -- which began on Saturday -- has prompted speculation in the West that the manoeuvres could be in preparation for a new attack on Ukraine.
The last time Belarusian and Russian forces held joint exercises was in February. Many of those Russian forces went on to cross the Ukrainian border in their ill-fated push to capture Kyiv.
The exercises were announced last week by Belarussian President Alexander Lukashenko who said his country and Russia would form a joint regional force.
Ukraine and Belarus share a large 1,000-kilometre border, which is largely wooded and unpopulated.
Concerns have also been raised that there could be a mobilisation of Belarussian reservists, although senior military officers in Belarus have dismissed this.
"All the fake information that is now published in various internet channels is not reliable, there is no reason to worry about it," claimed Alexander Shalpuk, a senior Belurassian officer, responsible for mobilisation.
"Citizens will be summoned to the military commissariat, their data will be noted, and they will depart to their place of work or place of residence. Mobilisation in the Republic of Belarus is not being carried out," he added.
The Belarussian opposition leader in exile said it would be a big mistake for Minsk to follow in the Kremlin's footsteps and announce a national draft.
"Neither the Belarusians nor the Belarusian army support this war," claimed Sviatlana Tsikhanouskaya,
"I doubt that Belarusian soldiers will participate in this call. They are not motivated in any way and, in fact, they are also not well equipped."
But Ukraine is not taking any chances.
If Ukraine’s long northern border with Belarus became a new line of attack it could put pressure on the country's military forces, particularly as the first stage of Russia's offensive was launched from Belarusian soil.
Ukraine has reinforced its defences along the border with special forces, who are currently training to counter any move by a possible joint Russian-Belarussian operation.